Touch Sensor, Liquid Crystal Display Panel Having the Same and Driving Method for the Same

1. A touch sensor installed inside a liquid crystal display panel that displays an image, the touch sensor comprising: a light sensing part to generate a control signal corresponding to a variation in external light when the liquid crystal display panel is touched; a capacitance sensing part comprising a liquid crystal capacitor to change the control signal according to a variation of capacitance when the liquid crystal display panel is touched; and a sensing signal output part to generate a sensing signal in response to the control signal and decide an output timing of the sensing signal, wherein the capacitance varies according to a change in cell gap of the liquid crystal capacitor.

2. The touch sensor of claim 1 , wherein the light sensing part comprises a photodiode connected to the liquid crystal capacitor.

3. The touch sensor of claim 2 , further comprising a coupling capacitor to change the control signal according to a ratio between a capacitance of the coupling capacitor and a capacitance of the liquid crystal capacitor, wherein the photodiode, the liquid crystal capacitor, and the coupling capacitor are all connected to a first node.

4. The touch sensor of claim 3 , further comprising: a first signal line connected to a first electrode of the coupling capacitor and an anode of the photodiode, the first signal line to receive a reset signal; a second signal line to apply a readout signal to the sensing signal output part; and a readout line to output the sensing signal, and wherein a cathode of the photodiode and a second electrode of the coupling capacitor are connected to the first node.

5. The touch sensor of claim 4 , wherein the first signal line and the second signal lines comprise an n th gate line and an (n−1) th gate line of gate lines arranged in the liquid crystal display panel, respectively, where n is a natural number equal to or greater than 2, the reset signal corresponds an n th gate signal applied to the n th gate line in an i th frame (i is a natural number equal to or greater than 1), and the readout signal corresponds to an (n−1) th gate signal applied to the (n−1) th gate line in an (i+1) th frame.

6. The touch sensor of claim 4 , wherein the sensing signal output part comprises: a first transistor connected to the first node to output the sensing signal in response to the control signal; and a second transistor connected to the first transistor to switch the sensing signal output from the first transistor in response to the readout signal.

7. The touch sensor of claim 6 , wherein the first transistor comprises: a control terminal connected to the first node; an input terminal connected to a driving voltage line to which a driving voltage is applied; and an output terminal connected to the second transistor, and wherein the second transistor comprises: an input terminal connected to the output terminal of the first transistor; a control terminal connected to the second signal line; and an output terminal connected to the readout line.

8. The touch sensor of claim 3 , wherein a cathode of the photodiode is connected to the first node, and an anode of the photodiode arranged in the liquid crystal display panel is connected to a common voltage line to which a driving voltage is applied.

9. The touch sensor of claim 8 , further comprising: a first signal line connected to a first electrode of the coupling capacitor, the first signal line to receive a reset signal; a second signal line to apply a readout signal to the sensing signal output part; and a readout line to output the sensing signal, and wherein a second electrode of the coupling capacitor is connected to the first node.

10. The touch sensor of claim 9 , wherein the first signal line and the second signal line comprise an n th gate line and an (n−1) th gate line of gate lines arranged in the liquid crystal display panel, respectively.

11. The touch sensor of claim 9 , wherein the sensing signal output part comprises a first transistor and a second transistor, the first transistor comprises a control terminal connected to the first node, an input terminal connected to a driving voltage line to which a driving voltage is applied, and an output terminal connected to the second transistor, and the second transistor comprises an input terminal connected to the output terminal of the first transistor, a control terminal to receive the readout signal, and an output terminal connected to the readout line.

12. The touch sensor of claim 11 , further comprising a third transistor comprising a control terminal connected to the first signal line, an input terminal connected to the driving voltage line, and an output terminal connected to the first node.

13. The touch sensor of claim 3 , further comprising: a first signal line to receive a switching signal; a second signal line to receive a reset signal; a driving voltage line to receive a driving voltage having the same phase and the same pulse shape as those of the reset signal; and a readout line to output the sensing signal.

14. The touch sensor of claim 13 , wherein a first electrode of the coupling capacitor and a cathode of the photodiode are connected to the driving voltage line, and a second electrode of the coupling capacitor and an anode of the photodiode are connected to the first node.

15. The touch sensor of claim 14 , wherein the sensing signal output part comprises a first transistor comprising a control terminal connected to the node, an input terminal connected to the driving voltage line, and an output terminal connected to the readout line, and wherein the first transistor outputs the sensing signal to the readout line in response to the control signal.

16. The touch sensor of claim 15 , further comprising a second transistor comprising a control terminal connected to the first signal line, an input terminal connected to the second signal line, and an output terminal connected to the first node, wherein the second transistor outputs the reset signal to the first node in response to the switching signal.

17. The touch sensor of claim 13 , wherein the first signal line corresponds to an n th gate line of gate lines arranged in the liquid crystal display panel and receive an n th gate signal as the switching signal, and the second signal lines corresponds to an (n−1) th gate line of the gate lines and receive an (n−1) th gate signal as the reset signal.

18. The touch sensor of claim 1 , wherein the light sensing part comprises a phototransistor, and the capacitance sensing part comprises a liquid crystal capacitor connected to the phototransistor.

19. The touch sensor of claim 18 , further comprising a coupling capacitor to change the control signal according to a ratio between a capacitance of the coupling capacitor and a capacitance of the liquid crystal capacitor, wherein the phototransistor, the liquid crystal capacitor, and the coupling capacitor are all connected to a first node.

20. The touch sensor of claim 19 , further comprising: a first signal line connected to a first electrode of the coupling capacitor and an input terminal of the phototransistor, the first signal line to receive a reset signal; a second signal line to apply a readout signal to the sensing signal output part; a third signal line connected to a control terminal of the phototransistor to apply a switching signal to the phototransistor, and wherein an output terminal of the phototransistor and a second electrode of the coupling capacitor are connected to the first node.

21. The touch sensor of claim 20 , wherein the second signal line and the third signal line comprise an (n−1) th gate line and an n th gate line of gate lines arranged in the liquid crystal display panel, respectively, where n is a natural number equal to or greater than 2, the switching signal corresponds to an n th gate signal applied to the n th gate line in an i th frame (i is a natural number equal to or greater than 1), and the readout signal corresponds to an (n−1) th gate signal applied to the (n−1) th gate line in an (i+1) th frame.

22. The touch sensor of claim 20 , wherein the sensing signal output part comprises: a first transistor connected to the first node to output the sensing signal in response to the control signal; and a second transistor connected to the first transistor to switch the sensing signal output from the first transistor in response to the readout signal.

23. The touch sensor of claim 22 , wherein the first transistor comprises: a control terminal connected to the first node; an input terminal connected to a driving voltage line to which a driving voltage is applied; and an output terminal connected to the second transistor, and wherein the second transistor comprises: an input terminal connected to the output terminal of the first transistor; a control terminal connected to the second signal line; and an output terminal connected to the readout line.

24. A liquid crystal display, comprising: a liquid crystal display panel comprising a plurality of gate lines, a plurality of data lines, a plurality of thin film transistors, each thin film transistor being connected to a corresponding gate line and a corresponding data line, and a plurality of first liquid crystal capacitors respectively connected to the thin film transistors to display an image; and a touch sensor to sense a variation in external light and a variation in cell gap to sense a touch event, the touch sensor being installed in the liquid crystal display panel, wherein the touch sensor comprises: a light sensing part to generate a control signal corresponding to of the variation in external light when the liquid crystal display panel is touched; a capacitance sensing part comprising a liquid crystal capacitor to change the control signal according to a variation in capacitance when the liquid crystal display panel is touched; and a sensing signal output part to generate a sensing signal in response to the control signal and decide an output timing of the sensing signal˜ wherein the capacitance varies according to a change in cell gap of the liquid crystal capacitor.

25. The liquid crystal display of claim 24 , wherein the light sensing part comprises a photodiode connected to the liquid crystal capacitor.

26. The liquid crystal display of claim 25 , further comprising a coupling capacitor to change the control signal according to a ratio between a capacitance of the coupling capacitor and a capacitance of the liquid crystal capacitor, wherein the photodiode, the liquid crystal capacitor, and the coupling capacitor are all connected to a first node.

27. The liquid crystal display of claim 26 , further comprising: a first signal line connected to a first electrode of the coupling capacitor and an anode of the photodiode, the first signal line to receive a reset signal; and a second signal line to apply a readout signal to the sensing signal output part, wherein a cathode of the photodiode and a second electrode of the coupling capacitor are connected to the first node.

28. The liquid crystal display of claim 27 , wherein the first signal line and the second signal line comprise an n th gate line and an (n−1) th gate line of gate lines arranged in the liquid crystal display panel, respectively, where n is a natural number equal to or greater than 2, the reset signal corresponds an n th gate signal applied to the n th gate line in an i th frame (i is a natural number equal to or greater than 1), and the readout signal corresponds to an (n−1) th gate signal applied to the (n−1) th gate line in an (i+1) th frame.

29. The liquid crystal display of claim 24 , wherein the light sensing part comprises a phototransistor, and the capacitance sensing part comprises a liquid crystal capacitor connected to the photodiode.

30. The liquid crystal display of claim 29 , wherein the thin film transistor and the phototransistor comprise n-type amorphous silicon.

31. The liquid crystal display of claim 29 , further comprising a coupling capacitor to change the control signal according to a ratio between a capacitance of the coupling capacitor and a capacitance of the liquid crystal capacitor, wherein the phototransistor, the liquid crystal capacitor, and the coupling capacitor are all connected to a first node.

32. The liquid crystal display of claim 31 , further comprising: a first signal line connected to a first electrode of the coupling capacitor and an input terminal of the phototransistor, the first signal line to receive a reset signal; a second signal line to apply a readout signal to the sensing signal output part; and a third signal line connected to a control terminal of the phototransistor to apply a switching signal to the phototransistor, and wherein an output terminal of the phototransistor and a second electrode of the coupling capacitor are connected to the first node.

33. The liquid crystal display of claim 32 , wherein the second signal line and the third signal line comprise an (n−1) th gate line and an n th gate line of gate lines arranged in the liquid crystal display panel, respectively, (n is a natural number equal to or greater than 2), the switching signal corresponds to an n th gate signal applied to the n th gate line in an i th frame (i is a natural number equal to or greater than 1), and the readout signal corresponds to an (n−1) th gate signal applied to the (n−1) th gate line in an (i+1) th frame.

34. The liquid crystal display of claim 32 , further comprising: an external luminance sensing part to sense an external luminance; and a voltage variable part to vary a voltage level of the reset signal applied to the first signal line according to the external luminance.

35. The liquid crystal display of claim 34 , wherein the voltage variable part comprises: a look-up table to store a voltage value of the reset signal according to the external luminance; and a voltage converting circuit to change the voltage level of the reset signal to a voltage value corresponding to the sensed external luminance.

36. A method of driving a touch sensor, comprising: generating a control signal corresponding to a variation in external light using a photodiode installed in a liquid crystal display panel when the liquid crystal display panel is touched; changing the control signal based on a variation in capacitance using a liquid crystal capacitor installed in the liquid crystal display panel when the liquid crystal display panel is touched; generating a sensing signal in response to the control signal; and outputting the sensing signal, wherein the capacitance varies according to a change in cell gap of the liquid crystal capacitor.

37. The method of claim 36 , further comprising resetting a first node in response to a reset signal, to which the liquid crystal capacitor and the photodiode are coupled, before generating the control signal.

38. The method of claim 37 , wherein the control signal changes according to a ratio between the capacitance of the liquid crystal capacitor and a capacitance of a coupling capacitor connected to the first node.